Hank, try also googling 68999 coax and you'll get a little more. Is
there nothing you can identify as a manufacturer's name or logo?

You should be able to estimate the loss pretty accurately from the
size, and you should be able to measure the impedance with enough
accuracy for amateur use pretty easily. Resonance and physical length
will tell you the propagation velocity, if you need that.

I'd guess it to be Teflon-insulated and Teflon-jacketed. Does it
matter a whole lot for what you want to do with it?

Cheers,
Tom